A combustion space subjected to high thermal and/or thermomechanical loading, such as, for example, a kiln, a hot-gas duct or a combustion chamber of a gas turbine, in which combustion space a hot medium is generated and/or directed, is provided with an appropriate lining for protection from excessively high thermal stressing. The lining normally consists of heat-resistant material and protects a wall of the combustion space from direct contact with the hot medium and from the high thermal loading associated therewith.
U.S. Pat. No. 4,840,131 relates to the fastening of ceramic lining elements to a wall of a kiln. There is a rail system here which is fastened to the wall. The lining elements have a rectangular shape with a planar surface and are made of heat-insulating, refractory, ceramic fiber material.
U.S. Pat. No. 4,835,831 likewise deals with the application of a refractory lining to a wall of a kiln, in particular to a vertically arranged wall. A layer consisting of glass, ceramic or mineral fibers is applied to the metallic wall of the kiln. This layer is fastened to the wall by metallic clips or by adhesive. A wire netting having honeycomb meshes is applied to this layer. The mesh netting likewise serves to prevent the layer of ceramic fibers from falling down. A uniformly closed surface of refractory material is additionally applied by being fastened by means of a bolt. The method described largely avoids a situation in which refractory particles striking during the spraying are thrown back, as would be the case when directly spraying the refractory particles onto the metallic wall.
A ceramic lining of the walls of combustion spaces subjected to high thermal stress, for example of gas turbine combustion chambers, is described in EP 0 724 116 A2. The lining consists of wall elements of structural ceramic with high temperature stability, such as, for example, silicon carbide (SiC) or silicon nitride (Si3N4). The wall elements are mechanically fastened elastically to a metallic supporting structure (wall) of the combustion chamber by means of a central fastening bolt. A thick thermal insulating layer is provided between the wall element and the wall of the combustion chamber, so that the wall element is at an appropriate distance from the wall of the combustion chamber. The insulating layer, which is approximately three times as thick as the wall element, is made of ceramic fiber material which is prefabricated in blocks. The dimensions and the external form of the wall elements can be adapted to the geometry of the space to be lined.
Another type of lining of a combustion space subjected to high thermal loading is specified in EP 0 419 487 B1. The lining consists of heat shield elements which are mechanically mounted on a metallic wall of the combustion space. The heat shield elements touch the metallic wall directly. In order to avoid excessive heating of the wall, e.g. as a result of direct heat transfer from the heat shield element or due to the ingress of hot medium into the gaps formed by the heat shield elements adjacent to one another, cooling or sealing air is admitted to the space formed by the wall of the combustion space and the heat shield element. The sealing air prevents hot medium from penetrating as far as the wall and at the same time cools the wall and the heat shield element.
WO 99/47874 relates to a wall element for a combustion space and to a combustion space of a gas turbine. Specified in this case is a wall segment for a combustion space to which a hot fluid, e.g. a hot gas, can be admitted, this wall segment having a mechanical supporting structure and a heat shield element fastened to the mechanical supporting structure. Fitted in between the metallic supporting structure and the heat shield element is a deformable separating layer which is intended to absorb and compensate for possible relative movements of the heat shield element and the supporting structure. Such relative movements can be caused, for example, in the combustion chamber of a gas turbine, in particular an annular combustion chamber, by different thermal expansion behavior of the materials used and by pulsations in the combustion space, which may arise during irregular combustion for generating the hot working medium. At the same time, the separating layer causes the relatively inelastic heat shield element to rest more fully over its entire surface on the separating layer and the metallic supporting structure, since the heat shield element penetrates partly into the separating layer. The separating layer can thus compensate for unevenness at the supporting structure and/or the heat shield element, which unevenness is related to production and may lead locally to unfavorable concentrated introduction of force.
In particular in the case of walls of high-temperature gas reactors, such as, for example, of gas-turbine combustion chambers operated under pressure, their supporting structures must be protected against a hot gas attack by means of suitable combustion chamber linings. Compared with metallic materials, ceramic materials are ideally suitable for this purpose on account of their high thermal stability, corrosion resistance and low thermal conductivity.
On account of material-specific thermal expansion properties under temperature differences typically occurring in the course of operation (ambient temperature during stoppage, maximum temperature at full load), the thermal mobility of ceramic heat shields as a result of temperature-dependent expansion must be ensured, so that no thermal stresses which destroy components occur due to restriction of expansion. This can be achieved by the wall to be protected from hot gas attack being lined by a multiplicity of ceramic heat shields limited in their size, e.g. heat shield elements made of an engineering ceramic. As already discussed in connection with EP 0 419 487 B1, appropriate expansion gaps must be provided between the individual ceramic heat shield elements, which expansion gaps, for safety reasons, must also be designed so that they are never completely closed in the hot state. In this case, it has to be ensured that the hot gas does not excessively heat the supporting wall structure via the expansion gaps. The simplest and safest way of avoiding this in a gas-turbine combustion chamber is the flushing of the expansion gaps with air, what is referred to as “sealing-air cooling”. The air which is required anyway for cooling the retaining elements for the ceramic heat shields can be used for this purpose.